The present invention generally relates to a compressor and more particularly, to a vane type rotary compressor, for example, for use in an air conditioning apparatus for motor vehicles and the like.
Conventionally, in a vane type rotary compressor, there has been employed means which depresses or urges the vanes so as to bring them into pressure contact with a cylinder wall by feeding pressurized lubricating oil at a high pressure generated at a discharge side of the compressor into bottom portions of vane grooves, and which means simultaneously lubricates the end faces of the rotor, the sliding faces between the vanes and rotor, etc.
The known arrangement as described above, however, has such disadvantages that, upon shutting down of the compressor, part of the lubricating oil is caused to continue to flow towards the bottom portions of the vane grooves by the high pressure remaining at the discharge side of the compressor, and that excessive lubricating oil tends to flow into the cylinder through the gap between the end faces of the rotor and side plate constituting the side wall of the cylinder or the clearance between the vanes and the vane grooves for further advancing towards the low pressure side in the cylinder. Accordingly, the rotor is subjected to reverse rotation by the flow of the lubricating oil as described above, and the leaking oil is also directed towards the suction pipe, and thus, abnormal pressure is built up in the cylinder due to compression of the oil during re-starting of the compressor, resulting in serious problems such as breakage of the vanes and rotor or deformation of the discharge valve, etc.
In order to overcome the disadvantages as described above, there has heretofore been proposed one system in which, by directing attention to the pressure difference before and after the discharge valve which is particularly conspicuous at the starting and stopping of the compressor, there is provided, in a lubricating oil passage, an on-off valve actuated by the above pressure difference, and arranged to open the lubricating oil passage during operation of the compressor and to close said lubricating oil passage upon shutting down thereof. Although the above prior art arrangement has a certain beneficial effect, it has been known that, in the vane type rotary compressors, the state of the refrigerant gas to be discharged upon one rotation of the rotor is such that a pressure difference is built up in the gas within the compression chamber before and after the vanes pass the outlet for the gas pressure in the compression chamber which causes development of pulsations equivalent to the number of vanes, thus resulting in momentary inversion of the pressure difference before and after the discharge valve. Accordingly, the on-off valve in the lubricating oil passage is caused to vibrate at high speed so as to shut off the oil passage in some cases, giving rise to various problems such as a "jumping" phenomenon of the vanes due to insufficient supply of the lubricating oil towards the bottom portions of the vane grooves, generation of noises, etc.